This invention relates to a semisubmersible tender adapted for facilitating servicing of off shore oil and natural gas production platforms, subsea wells, and other subsea infrastructure in water depths up to 10,000 feet.
The present invention specifically relates to a semisubmersible tender which can be secured to different types of production platforms, such as a tension leg platform (TLP), a deep draft cassion vessel (SPAR), a fixed platform, a compliant tower, a semisubmersible production vessel, or a floating vessel.
It is very expensive to provide a production platform with adequate space for all the drilling and completion equipment needed to safely drill and complete a well and store drilling and completion equipment and materials in an environmentally conscientious manner, including drilling and completion risers, casings, tubings and drilling and completion fluids. Tenders have often been called into service to provide the required space needed on a rig and/or platform during the initial drilling and completion phase of an oil lease. Problems have traditionally existed in that most tenders cannot be kept alongside a platform in a constant spaced relationship during extreme weather without colliding with the platform. Specifically, tenders have not been able to remain in a connected capacity and avoid the risk of collision, enabling a high operational weather window to the tender and rig, and still endure the environmental load of up to a 10 year storm. See U.S. Pat. Nos. 4,065,934, and 4,156,577, which are hereby incorporated by reference on current tenders for platforms. Most tenders have had to be completely towed away to a safe location in the case of a tropical storm or extreme weather, which causes considerable expense to the drilling contractor and/or customer.
Until the existence of this invention described herein, it has been generally believed to be impossible to safely moor a tender to a floating production platform in water depths exceeding several hundred feet for long periods of time, exceeding one year or any time during hurricane season.
The present invention has been created to provide up to 25,000 square feet of additional deck space and over 8000 bbls of liquid storage capacity via a tender which is secured to the production platform by a unique technique which enables the tender to keep a constant distance from a production platform while synchronizing its low and mean movement frequencies, which enables the tender to follow the mooring watch pattern of the production platform, such as a figure eight pattern, or elliptical pattern, and to sustain without damage, the environmental load of wind, current and wave forces of a 100-year cyclonic storm (such as a hurricane) in the 100-year extreme weather standby position, and up to a 10-year storm in a tendering position.
The invention is related to a device, which has significant environmental and safety advantages over known systems and known tenders.
The invention includes the semisubmersible tender, a tender and mooring system which utilizes pre-set anchors, and a method of tendering to a deep-water production platform for assisting in the drilling and completion and recovery of oil and gas in weather that can be up to a 10-year storm and maintaining a standby position in weather up to a 100-year hurricane.
The present invention is directed to solving one or more of the above problems by providing a tender for facilitating installation operational support and removal of drilling and completion equipment on a production platform while compensating for platform motions in at least one plane.
The invention relates to a tender, and a mooring and tender system for securing a unique semisubmersible tender to a production platform. The semisubmersible tender has mooring means and a lightship displacement of less than 15,000 short tons and preferably between at least 8,000 and 15,000 short tons. The tender comprises a deck; a shape that results in a combined environmental load of less than 1000 kips in a 100-year extreme weather condition; a plurality of supports connected to the deck; a plurality of pontoons connecting the supports; at least two hawsers for connecting the tender to the production platform, each hawser having a length which is selected from the group: the length of the tender, the tendering distance, the length of the production platform, and combinations thereof; and wherein the hawsers have adequate elasticity to accommodate the wave frequency motions between the production platform and the tender, and adequate stiffness and tension to synchronize the mean and low frequency movement between the production platform and the tender under an environmental load produced during a storm having a designation of up to a 10-year storm in the tendering position.
This invention permits the tender to remain connected to the platform yet the hawsers remain slack during a storm designated as at least a 10-year storm for the tender in the tender standby position. The tender further has connecting means securing a first end of each hawser, and a hawser guidance system for each hawser to direct each hawser to the production platform.
The tender uses an at least 8-point mooring system for the tender which uses at least 8 anchors; at least 8 mooring lines, with each line consisting of: a first length of steel wire rope secured to each of the anchors; a length of polymer rope secured to each of the first length of steel wire rope; a second length of steel wire rope having a first and second end, and wherein the first end is secured to the length of polymer rope and the second end is secured to the tender. For the invention, each mooring line has adequate elasticity, stiffness and strength to accommodate load on the tender under an environmental load produced by an up to a 10-year storm in the tendering position, and further wherein the mooring lines have a strength to withstand the environmental load produced by up to a 100-year extreme weather condition when the tender is moved to a 100-year extreme weather condition standby position. The tender further has means for creating global equilibrium between the production platform""s mooring means and the at least 8 point mooring system of the tender.